The wig is definitely more noticeable this season than last, and it's likely due to COVID. Michael Michele has been very vocal about her stance on COVID, etc. so she has probably chosen to spend less time in the hair department is what I am guessing. Especially since I'm pretty sure her actual hair was used during the second and majority of the third seasons.
Where did that come from? Especially since the season just wrapped filming, it's far too soon for promotional campaigns to be unveiled. Either way, it wouldn't be the first time Bravo re-used the same promotional portraits for different seasons.